Virginia Tomás

Simultaneous determination of propranolol and pindolol by synchronous spectrofluorimetry

The simultaneous determination of propranolol and pindolol using synchronous fluorescence spectrometric techniques is described. The method involves measuring the natural fluorescence of these drugs in a 50% (v/v) ethanol-water medium using zero and first derivative synchronous spectrofluorimetry. Under the optimum conditions, the linear determination ranges of propanolol and pindolol are ca. 0.02-1.0 and 0.04-1.2 mug ml(-1), respectively. The results showed that propranolol and pindolol can be determined simultaneously when the concentration ratio of propranolol to pindolol varies from 1:100 to 50:1 in the mixed sample. The method has been satisfactorily applied to the determination of propranolol and pindolol in urine samples and propranolol in pharmaceutical preparations.

Flow-injection fluorimetric determination of penicillamine and tiopronin in pharmaceutical preparations

Two flow-injection methods for the fluorimetric determination of penicillamine and tiopronin are proposed. The procedures are based on the oxidation of these drugs by thallium(III). In hydrochloric acid medium the fluorescence of thallium(I) formed in the oxidation of penicillamine or tiopronin is monitored using excitation and emission wavelengths of lambda ex = 227 nm and lambda em = 419 nm respectively. Linear calibration graphs were obtained between 3 x 10(-7) and 8 x 10(-6) M for penicillamine and between 8 x 10(-7) and 2 x 10(-5) M for tiopronin with sampling frequencies of 90 and 45 samples h-1 respectively. The relative standard deviations were in the ranges 0.48-0.29% for penicillamine and 1.04-0.31% for tiopronin. The applicability of the method to the determination of both drugs in pharmaceutical preparations was demonstrated by investigating the effect of potential interferences and by analysis of commercial preparations.

Analysis of binary mixtures of flufenamic, meclofenamic and mefenamic acids by derivative synchronous fluorescence spectrometry

Second-derivative synchronous fluorescence spectrometry was used to develop a simple, rapid and sensitive spectrofluorimetric method for the determination of binary mixtures of the nonsteroidal antiinflammatory drugs flufenamic (FFA), meclofenamic (MCFA) and mefenamic (MFA) acids in serum and pharmaceutical formulations. The method is based on the intrinsic fluorescence of these compounds in chloroform. A Deltalambda=105 nm was used for the resolution of FFA-MFA and MFA-MCFA mixtures, whereas the FFA-MCFA mixture was determined at Deltalambda=40 nm. Serum samples are treated with trichloroacetic acid to remove the proteins, and the analytes are extracted in chloroform prior to determination. Pharmaceutical preparations were analysed without prior separation steps.

Flow-injection fluorimetric determination of trimeprazine and trifluoperazine in pharmaceutical preparations

A flow-injection configuration for the fluorimetric determination of trimeprazine and trifluoperazine is proposed. The procedure is based on oxidation of the drugs by cerium(IV). The fluorescence of cerium(III) formed in the oxidation of trimeprazine or trifluoperazine is monitored. Lineal calibration graphs were obtained between 2 x 10(-7) and 1 x 10(-5)M for both trimeprazine and trifluoperazine with a sampling rate of 60 samples/hr. The relative standard deviations were over the ranges 0.78-1.16 and 0.84-0.97% for trimeprazine and trifluoperazine respectively. The applicability of the method to determination of trimeprazine and trifluoperazine was demonstrated by investigating the effect of potential interferences and by analysis of commercial pharmaceutical preparations.

Flow injection fluorimetric determination of thiamine and copper based on the formation of thiochrome

The reaction, involving the oxidation of thiamine by copper(II) in basic solutions to fluorescent thiochrome, has been adapted to the determination of thiamine by flow-injection analysis. Linear calibration graphs are obtained between 0.30 and 6.02 mug/ml with a sampling rate of 50 samples/hr and a relative standard deviation of 0.53%. This reaction has also been adapted to the determination of copper(II) over the range 0.5-5.0 mug/ml. The applicability of both methods for determination of thiamine and copper is demonstrated by investigating the effect of potential interferences and by the analysis of real samples (pharmaceuticals for thiamine and ores and alloys for copper).

Determination of epinephrine, norepinephrine dopamine and L-dopa in pharmaceuticals by a photokinetic method

A study of the photochemical reaction of the Rose Bengal (RB)-ethylenediaminetetraacetic acid system in the presence of epinephrine, norepinephrine, dopamine and L-dopa is presented. The rate of photoreduction of RB is dramatically retarded by small amounts of these catecholamines, which have an inhibitory effect on the excited state of RB, which is the activator of the process. Optimum conditions for the determination of catecholamines in the range of concentration between 5 x 10(-6) and 1 x 10(-4) mol dm-3 are described. The proposed method has been applied with excellent results to the determination of catecholamines in pharmaceuticals.

Direct determination of ranitidine and famotidine by CE in serum, urine and pharmaceutical formulations

A simple and sensitive capillary electrophoresis method using UV detection has been developed for the direct determination of ranitidine (RANT) and famotidine (FAMT) in serum, urine and pharmaceutical formulations. A buffer consisting of 60 mM phosphate buffer adjusted to pH 6.5 was found to provide a very efficient and stable electrophoretic system for the analysis of both drugs. The detection limits obtained were 0.088 microgram ml(-1) for RANT and 0.16 microgram ml(-1) for FAMT.

Fluorimetric determination of total ascorbic acid by a stopped-flow mixing technique

A simple, rapid and automatic fluorimetric method for the determination of total ascorbic acid is described. The method makes use of the stopped-flow mixing technique in order to achieve the rapid oxidation of ascorbic acid by dissolved oxygen to dehydroascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The initial rate and fluorescence signal of this system are directly proportional to the ascorbic acid concentration. The calibration graph was linear over the range 0.1-30 microg ml(-1) (kinetic method) and 0.25-34 microg ml(-1) (equilibrium method). The precision (% RSD) was close to 0.5%. The method has been used for the determination of ascorbic acid in pharmaceutical formulations, fruit juices, soft drinks and blood serum.

Simultaneous determination of diquat and paraquat residues in various matrices by capillary zone electrophoresis with diode array detection

SummaryThe separation of diquat and paraquat by CZE has been investigated. The addition of acetonitrile (10 %, v/v) to a phosphate buffer (100 mM, pH 4.0) is necessary for effective separation of both herbicides at an optimum applied voltage of around 12 kV; the current and migration times were stable and reproducible under these conditions. The method was validated for linearity and reproducibility. The detection level calculated for diquat and paraquat was 30 and 40 nM, respectively in the injection solution. By use of stacking, these detection levels were improved by a factor of 120. The method is suitable for the determination both herbicides in samples such as herbicidal formulations, water, soil, potatoes, urine and serum. Photodiode-array detection permitted the rapid identification of both compounds.

Photochemical spectrophotometric determination of riboflavin and riboflavin 5′-phosphate by manual and flow injection methods

The sensitizing effect of riboflavin (RF) and riboflavin 5′-phosphate (FMN) on the photo-oxidation of dianisidine was studied. The rate of the photochemical reaction was monitored spectrophotometrically at 460 nm. The method allows the determination of RF and FMN in the range 1 × 10–7–5 × 10–6 mol dm–3 with a relative standard deviation of about 0.68%. The method can be successfully adapted to flow injection. Manual and flow injection methods were satisfactorily applied to the determination of RF or FMN in fortified breads and pharmaceutical preparations. A possible mechanism for the sensitized photoreaction is proposed.